Accumulator tanks

[farlet]

Hello, We live in Sweden in the North, so heating is very important !

We have a large wood furnace in the basement which heats water for the radiators. It is an old system with big bore pipes and it works without any pump, just gravity. I have been given 2 x 300 litre accumulator tanks which are insulated and I would like to try and incorporate them into the system to keep the house warm for longer after the furnace goes out. Everyone else I know with accumulator tanks uses a pumped system with two circuits, one for the furnace and accumulator tanks and one for the radiators.

Does anyone know how well it would function if I just plumbed them into my existing circuit ? I was thinking that they could be plumbed straight into the furnace so that the hot water comes out of the furnace and into the tanks first. Am I going to get any benefit ? Is there a better system which would keep it simple with no pumps ?

Thanks for any help

[mapleveneer]

I think that you will find it quite challenging to make such an arrangement work.  First, the big bore pipes that you currently have, do they all pitch slightly upward from the boiler to the radiators?  I suspect so, as this will enhance the gravity circulation of the water.  The heated water likes to rise, not go downhill in any section of piping.  If that is the case, then you would need to install your supplemental heat storage tanks with the inlet at the bottom and the outlet at the top.  The inlet will need to be above the level of the outlet at the top of your boiler and the outlet from the tank will need to be below the level of your lowest radiator.  For two tanks to work they would need to be in series with the inlet of the second above the outlet of the first only further compounding your problem.

[farlet]

Hello, thanks for the reply.

So if I could find somewhere to put the tanks higher than the outlet of the furnace, it would work ? I can do this, but it would be quite a bit of work, am I going to get a big benefit from just having them inline in the standard system like this ?

I dont want to create a whole load of work without much benefit

Thanks again

[r.man]

Farlet my advice would be to pipe the new tanks into the old, as close as you can get them, without interfering with the existing rad pipes. This should increase your reservoir size and your heating capacity after the fire is out. Thermo-siphoning should be adequate for what you want but keep the pipe size as large as is convenient. Do it the easy way first and if that doesn't work try harder options.

[Gary_C]

Hello, We live in Sweden in the North, so heating is very important !

Is there a better system which would keep it simple with no pumps ?

Hello from Minnesota, the Sweden of the west.  ;D

The effective pump in your system is the temperature difference between the lower and upper levels of your home. Unless you increase that temperature difference, an increase in volume in the system may have little effect. Plus without a mechanical pump in the system you will have a lot of trouble getting the temperature of the water up in all of your tanks with out boiling the water in the furnace.

Without seeing your actual system layout, I would suspect you will be doing a lot of work for little benefit. Plus a trial and error installation to see what works is not a good idea either.

So my best answer to your question would be to put in the pump.

[farlet]

Thanks again for your replies.

The water temp in the radiators gets to about 60 degrees celcius, so I was assuming that the water in the tanks would get to this also if they were plumbed into the radiator circuit. Most of the year the system works great as it is and keeps the house very warm. Its just in January and December, we can get down to -45 celcius outside and in the mornings it is a little cold in the house until you light the furnace. I was hoping that the tanks would give us a few extra hours and it wouldnt be so bad in the morning. We get a few times a year when the storms take out the electric and because we are so remote, it is sometimes a week before we are back on, this is why I want to try and avoid the pump as typically you get a cold spell after the storm.

On a side note, we installed triple glazed windows this year, and the difference was phenomenal, such a difference.

I will draw a rough schematic and try and figure out how to post it and see if there is a simple solution worth pursuing.

Thanks

[Holmes]

  I agree with maple and r.man. .  Is about 135000 btu's of extra storage really any help?  maybe 2 hrs?   I think if the inlet are low and separate  and the outlets tie into a manifold , then go into the storage tank you may get the gravity feed you want.  Sounds interesting.   Gravity systems have been around forever they do work with out pumps as you well know.

[farlet]

I think if I got an extra 2 hours, it would make the world of difference. We fill up the furnace before bed, and I guess it burns until about 2am, so if this stretched to 4am, then there are only a few hours without a fire.

Any chance you can explain the bit about the inlets and outlets. Do I definitely need the tanks higher than the outlet on the furnace ? As I understand it, The hot is going to come from the furnace into the tanks at the bottom, out of the top of the tanks and into the radiator circuit, then the rest of the system remains unchanged. Is this right ?

Thanks

Tim

[Holmes]

  That sounds like the simplest way to do it.  Make certain  the tanks do not have built in thermal traps.  If the tappings are 3/4" ish I would increase the piping maybe to  1.25" ish.  Why?  I believe gravity systems function better with larger piping. All the gravity systems I worked on had large pipes.  Isolating the tanks from the original tank with ball valves will make redo's easier.

[Gary_C]

How do you control the fire in the furnace?

If you look at your system from an overall view, if you want to heat the house more hours, that will take more wood in the furnace. If the furnace is relatively balanced for your house, more heat will either require more hourly capacity or more hours.

More storage capacity for water will introduce more lag time in the system both on start up and after fire out. So more storage capacity may only move the cold hours from the fire out time to the morning on fire start time unless you increase flow in the system.

As far as I can see, more flow can only be accomplished with a pump, not more storage.

[Holmes]

 I believe farlet is not looking for more flow. He wants to add more storage and then make certain the added storage enters the heating system.

[Gary_C]

I believe farlet is not looking for more flow. He wants to add more storage and then make certain the added storage enters the heating system.

He is actually looking for more heat, not more storage. Storage does not equal heat.  :

[farlet]

I am pretty sure that during the day, there is spare capacity in the system as the house gets pretty hot. Actually, this is one of the downsides of the gravity setup in that it isnt very controllable, and you can get to where you have to open the windows in the middle of winter.

I can see what you mean about it taking a little longer to heat up in the morning, but I think it would be worth it for those extra hours in the night. We have a small stove in the living room which we can use to boost first thing in the morning.

In any case, we have unlimited supplies of free wood and we are setup for processing it, so its no problem if we burn a little more - maybe burn the furnace hotter prior to going to bed.

Another thing we are doing is improving the insulation each year, and this of course helps, but we are more or less at the practical limit of this now.

I think that I have to figure out the best way to get the tanks higher than the furnace and then the pipe it up and try. Thanks for all your help

[Holmes]

I believe farlet is not looking for more flow. He wants to add more storage and then make certain the added storage enters the heating system.

He is actually looking for more heat, not more storage. Storage does not equal heat.  :

The heat is stored in the tanks Gary. :P

[beenthere]

I am pretty sure that during the day, there is spare capacity in the system as the house gets pretty hot. Actually, this is one of the downsides of the gravity setup in that it isnt very controllable, and you can get to where you have to open the windows in the middle of winter.

.....................

IMO, you need to fix this problem first... and get some control of the distribution of the heat so the house doesn't get too hot and you don't have to open windows in the winter.

[farlet]

I dont mean that we open the windows every day, its just now and then when you let the furnace burn too hot. What I meant was that once you have done this, it takes a long while for it to come back down to a sensible temp hence the open windows

[Gary_C]

I am pretty sure that during the day, there is spare capacity in the system as the house gets pretty hot. Actually, this is one of the downsides of the gravity setup in that it isnt very controllable, and you can get to where you have to open the windows in the middle of winter.

I can see what you mean about it taking a little longer to heat up in the morning, but I think it would be worth it for those extra hours in the night. We have a small stove in the living room which we can use to boost first thing in the morning.

In any case, we have unlimited supplies of free wood and we are setup for processing it, so its no problem if we burn a little more - maybe burn the furnace hotter prior to going to bed.

I still don't understand how you control your wood stove.

Are you manually adjusting a damper on the air flow or is there an automatic water temperature control that sets the damper?

Or perhaps you don't have a control other than the amount of wood you put in the stove?

Do you have any control of water temperature?

[farlet]

Oh sorry, we control the temperature manually with the air dampener. It is quite basic and you have to get used to it. It heats the hot water for the taps as well and you cant take the water in the radiator system over 60 degrees C as it will boil the hot water for the taps.

[beenthere]

................. We get a few times a year when the storms take out the electric and because we are so remote, it is sometimes a week before we are back on, this is why I want to try and avoid the pump as typically you get a cold spell after the storm. ................

Thanks

Either put in pumps or zone valves that will let hot water flow through when you have electricity, and then switch to your gravity system when the electricity is off.
I have three zones that the pumps are turned on/off with thermostats. If the electricity goes off, I can open the back-flow preventing valves and let the system heat the house with gravity feed. Works pretty good. And I have only a 9 gal storage tank around my hot water wood boiler.

[Hilltop366]

Wondering if it would work to put a bypass around the extra storage to get heat faster in the morning then switch back to the tanks later to store your extra heat.

I have a samson draft control, it is non electric and works well. It requires a place to install in the boiler.

Also wondering what the triple glazed windows replaced.

[Gearbox]

I think you might plumb it into the boiler first top to top lower to lower and fire it up cold and get it up to temp and see what happens . All your out is a lot of water and some wood + pipe fittings . Go the easy way first . The other way cold water moves better than hot so put it into the return .Gearbox

[Gary_C]

OK, now I understand your system.

It's going to take more total BTU's to heat your house for more hours per day and since you are running your heat system at maximum capacity for the hours you are feeding the stove wood, you cannot get more hours of heat from your existing system. You could either add wood more hours per day or put in a larger firebox to hold more wood at a time.

If you add more storage, you will only shift the cold hours from night to morning. If that is acceptable as you can add other heat during the morning hours then the additional storage will work but it's going to be a lot of work to get the storage installed right.

If you do add the storage capacity, it's not necessary to have ever increasing heights on the tanks, but it's critically important to eliminate air at every high point in each tank as well as having large sized pipes to reduce flow restrictions. Plus of course having a closed system and the tanks in series, not parallel.

[John Mc]

This may be getting more complicated than you want, but I'm wondering if you want to put a bypass around your storage tanks. If you bypass thm in the morning, when you want a quicker response, you can heat just the water in your boiler and start circulating it around the house. Once the house is up to temperature, then you open the loop to include your storage tanks and start heating them up. (This might also help with the overheating during the day - if it gets too warm, dump some heat into the storage tanks.)

Another thing to consider: If you are limited to 60˚C so the water in your taps does not get too hot, have you considered adding a mixing valve to the line that feeds the hot water to your taps? (or to the output side of your hot water tank, if you have a separate tank that feeds your hot water taps.) Mixing valves take no power to operate. They take the incoming hot water, and mix it with enough cold water to get a preset output temperature for your hot water taps. All automatic. That would let you run your boiler at higher temperatures, without worrying about someone getting scalded from your tap water. Including a mixing valve is a requirement for new construction in my area.

[John Mc]

... It's going to take more total BTU's to heat your house for more hours per day and since you are running your heat system at maximum capacity for the hours you are feeding the stove wood, you cannot get more hours of heat from your existing system. You could either add wood more hours per day or put in a larger firebox to hold more wood at a time.

I don't think he is running it at its maximum capacity while he is feeding the stove wood. If this is the case, more storage will help him, if he can just figure out how to get the heat into and out of the storage when needed. That problem is rather simple, if you use pumps and electronic controls. It takes a bit more thought on how to accomplish this if you just want to use gravity/thermosiphon.

[Gary_C]

John, as I understand the system, his firing rate in the stove is limited by boiling in the hot water system. Unless he can change the ratio of the heat going into the two systems, he is stuck with the same firing rate. So the only way to get more heat in the house is to fill the stove more hours in the day.

It sounds like farlet has a very simple elegant system that cannot be altered without making it much more complex. The simple easy solution is to get up in the night and fill the stove. Easier said than done on a nightly basis.

[Holmes]

The other option is to collect heat from the day time burn , store that heat in the tanks . That energy will be released thru the night extending by a few hours the cooling off of the house. If he can figure out how to make the storage tanks work  in a gravity feed system.
  What is the size of the heating main? 3 to 4 inch?  Do you have a side arm tank less heater?    Any handy usefull tapping on the boiler to connect to or on the main?

[John Mc]

John, as I understand the system, his firing rate in the stove is limited by boiling in the hot water system. Unless he can change the ratio of the heat going into the two systems, he is stuck with the same firing rate. So the only way to get more heat in the house is to fill the stove more hours in the day.

I thought he had more capacity during the day. From reply #12:

I am pretty sure that during the day, there is spare capacity in the system as the house gets pretty hot. Actually, this is one of the downsides of the gravity setup in that it isnt very controllable, and you can get to where you have to open the windows in the middle of winter.

[John Mc]

I wonder if there is a way to use pumps on the loop for the storage tanks, while still keeping your existing system mostly as it is, allowing for gravity/thermosiphon operation?

This would mean in a power outage, you are no worse off than you are now, but when the power is on, you could use your storage system. You could have electronic controls which put heat into storage when there was excess capacity, and drew it back out when the house or boiler started to go cold.

[Gary_C]

I thought he had more capacity during the day. From reply #12:

I am pretty sure that during the day, there is spare capacity in the system as the house gets pretty hot. Actually, this is one of the downsides of the gravity setup in that it isnt very controllable, and you can get to where you have to open the windows in the middle of winter.

He backed away from that claim in reply #15:

I dont mean that we open the windows every day, its just now and then when you let the furnace burn too hot. What I meant was that once you have done this, it takes a long while for it to come back down to a sensible temp hence the open windows

Perhaps those too hot days were when the hot water system boiled?

It appears the bottom line is until you uncouple those two water systems, you cannot put more wood in the fire without extending the hours per day you run the system. The first law of thermodynamics (conservation of energy) tells us that you can't get more heat without adding more wood.

[Holmes]

John Mc I think that pump idea is a good one if he can't get the heat from the storage tanks by gravity. Placing a circulator in the wrong location could drive all the heat into the house very quickly.  I do understand how difficult this heating system is to control {perpetual manual dampering}, trying to get as much heating without boiling, not get to much heat in the mild days and control creosote.
One other item could be to give the house more thermal mass.  Can you radiant heat a concrete floor?

[farlet]

Good morning from Sweden. Very interesting, and it has made me think some more.

The hot water for the taps consists of 100 litres in the furnace, so separate tank, and a mixer valve which limits the temp out of the tap to 60 degrees C. This is what limits our temp on the radiators because the 100 litres will boil if you go over 60 on the tap water circuit. What if I added more capacity to the tap water circuit. It would be very easy to add another 150 litre tank to this system upstairs and this would gravity circulate and take some of the heat away from the tap water part of the furnace.

This would mean that in the coldest parts of winter, we could burn hotter before going to bed and get the radiator circuit up to 70 or even 80. This I am sure would have a big effect through the night.

What do you think ?

Someone was asking about the triple glazing. Before the triple glazing, we had old fashioned double glazing. In Sweden they are called cassette windows, they are two single glazed windows sandwiched together. Whilst they work OK and are draft free, the triple glazed windows are totally amazing. We have friends in the village with modern double glazing and when it goes below -40 C, theirs have ice inside on the bottom corners. At the same time, our triple glazed were warm to the touch inside.

[farlet]

Sorry, its early here and I typed a few errors on that last post.

Meant to say that there is no seperate tank for the tap water just the 100 litres in the furnace, and that the 100 litres will boil if the radiator circuit goes over 60.

[beenthere]

farlet
You can edit your post (click on "modify") and make it correct the way you wish it to read. Saves others trying to sort out the correction needed. No need to add another post. Have a good day.

[farlet]

Been thinking about this all day, and the more I think about it, I can see it being a great solution. We have another problem with the current system which is in the summer. The furnace is our only source of hot water, so we have to light it each day in the evening which is a pain. I have wanted to have a solar water heater for a long time and it is perfect here in the summer as we have 24 hour sun for nearly 3 months.

I have done a very rough schematic of the hot water circuit for the hot taps, 3 scenarios, 1st is as we are now, then two options for a new setup. I can buy a hot water tank for upstairs which has either 1 or 2 coils in it. 1 will obviously be for the solar heater as this will be a standalone setup, but which would be better for the furnace, option 1 or option 2 ? I can see option 1 being more effective at taking away the heat from the 100 litres in the furnace which is what we want in the cold winter so that we can burn hotter.

What are peoples thoughts on this ? Hopefully the picture works !

Thanks

 

[Gary_C]

Gravity fed systems are more art plus trial and error than anything else. Just from looking at your options, I cannot see how the water will circulate without a pump.

How is your cold water fed to your house? Is it thru a pump or gravity feed system? How much pressure?

I have an outdoor boiler and what they call a sidearm heater on my hot tap water tank. But the hot boiler water is fed thru a circulator pump on the outdoor boiler. From what I know of solar panels they require a circulator pump also. So I believe you are at the limits of what you can do to improve your gravity system without adding some pumps.

[farlet]

We have a well with a pump for the water. It is at about 25psi in the system. When the power goes off, then we dont have any water, but the radiator system works just fine.

In option 1 or 2, I thought that if I have big pipes between the furnace and the tank/Coils in tank, then it should circulate by gravity, is this not right ? The tank will be about 3 metres higher than the top of the furnace

From what I have read online, you can have a thermosiphon solar system which works on gravity if there is a good height between your collector and tank.

[Holmes]

  I like option 2. With that you are not using/ drinking your boiler water.  You can pressurize your boiler and increase the boiler water temperature.

[Holmes]

   They may make a non electric bulb controlled zone valve . You could install it in the feed line with the bulb/ sensor in the control well This would give you some control over the hot water so you could run the boiler hotter.

[stratton]

Hilltop, what kind of boiler do you have????.. The reason i ask is i have a d.s. aqua gem 3200.. it came with a sampson valve.Super simple design!!!!

[Hilltop366]

Tarm, it was made in 1978. It was unused until 2000 when I bought it.

[Holmes]

I put in quite a few Tarm boilers back in the 80, s.  A good product.

[mapleveneer]

In regards to the posted image of the domestic hot water setup above, i don't think option 1 or 2 will work as shown or if they do work it will move only very minimal heat.  They are both shown as having supply and return connections made to the top of the 100 litre tank.  This means that they will both be at the same temperature.  The hotter water is in the top of the tank and the cooler in the bottom.  A thermal syphon requires a temperature gradient to work.  The hot water is trying to rise through both pipes at the same time, so no circulation.  Check your existing connections on the gravity hot water heating system.  Does the supply connect to the top of the boiler and the return connect to the bottom?  I suspect so as this is how you get the gradient in that system.  My house had gravity hot air for 72 years so i know how to control the house temp by opening doors and windows also!

Circulator pumps draw very little current, typically 75-180 watts.  Equivalent to incandescent lights.  If your concern is loss of power to your circulator, buy a little DC to AC inverter.  Plug it into your car's power outlet and run an extension cord to your pump.  No need for big generators or even to maintain an extra battery.

I still think you are going to have a difficult time achieving a thermal syphon with storage tanks simply plumbed into your existing piping.  A few posts up someone mentions putting the tanks adjacent to your system and using a pump to circulate through them.  This suggestion might be worthy of further consideration.  You could manually control that pump to draw heat out of your system when it is too hot and to add heat to your system for those cool mornings.  And you can leave your existing system basically untouched so that it will continue to operate as it currently does.  You want to be careful that you don't shoot yourself in the foot by making a change that reduces or stops circulation.  The end result there would be little or no heat probably when you want it the most!